The present invention relates to safety devices for spray coating apparatus of the type which comprise a centrifugal sprayer member or head to which a rapid rotation is imparted, and in particular to a safety cover for the rotating head which both shields the same against accidental contact therewith by nearby personnel and acts as a receptacle for residual materials during changes in color of the coating materials.
Electrostatic spray coating systems have been successfully used in commerce in several different forms. For example, systems have been used which utilize spraying or atomizing devices employing hydraulic forces or air as the atomizing medium. In another type of system which does not require air or hydraulic forces for atomizing coating material, however, atomization is accomplished by means of a centrifugal sprayer member or head to which a rapid rotation is imparted. The head has a surface against which a stream or jet of liquid to be sprayed is directed, the liquid on striking the revolving surface progressing radially outwardly thereover in a thin film under centrifugal force toward a sharp annular peripheral edge of the head, whereat it is divided into fine particles so that it leaves the periphery in the form of a spray. For electrostatic deposition of the coating material the rotating head is of a conductive material and connected to a high d.c. potential, so that the spray particles on moving past the peripheral edge of the head are charged to a high electrostatic potential. The resulting ionized or electrostatically charged cloud of particles is then attracted to and settles on the surface of the articles or ware to be coated, which are usually maintained at ground potential.
Heretofore the spray heads of such electrostatic coating apparatus have been rotated at relatively low speeds, i.e., on the order of 3000 to 6000 rpm. However, recent developments contemplate rotating the heads at considerably greater speeds on the order of 30,000 to 60,000 rpm, which enhances both the atomization and flow rate of material sprayed from the head. Quite obviously, the sharp peripheral edges of spray heads rotated at such high speeds present a significant danger to nearby personnel who might accidentally contact the same. Although the danger of personal injury is somewhat less when the head is energized, since the head is normally rotated by an air turbine the noise of which is a warning, the danger increases upon deenergization of the head and for a period of time thereafter. That is, upon deenergization turbine noise ceases, yet because of inertia and the high speed of rotation, the head continues to rotate for a period of time at speeds which may still cause severe injury to a person contacting the same.
When used in industrial operations where articles are to be spray coated as they move along a production line, and where the articles are required to be coated a wide variety of colors, color change system are often used with rotary head spray coating apparatus, and enable different colored coating material to be sequentially sprayed from a single head. However, to effect a color change the head must first be cleansed of previously sprayed material, which is usually accomplished by introducing onto and spraying from the head a small amount of solvent for the material. To prevent the solvent and residual amounts of the previously sprayed material from being deposited on articles during the cleaning process, the prior art contemplates moving the spray apparatus to a position remote from the articles whereat the solvent and residual material may be sprayed from the head without being deposited on the articles. In the case where the articles conveyed past the coating station are closely spaced, the resulting time limitations imposed by the color change process often requires operation of the production line at a speed which is less than desirable or optimal.